The overall goal of this proposal is to understand how cells are able to produce specific responses to changes in their microenvironment. Often, such responses involve G protein coupled receptors and thus are dependent on G protein signaling. G proteins transduce the extracellular signals received by receptors into cellular responses. Both the G? and the G? subunits of G proteins propagate signaling by activating/inhibiting various effector molecules which then cause changes in cell function. The first effectors discovered to be mediated by G? were the G protein coupled inwardly rectifying K+(GIRK) channels. Previous studies have shown that G? can mediate several effects on currents conducted by GIRK channels. Mutation of specific residues on the channel or G? may inhibit some G? effects but leave others intact. Thus this pro G? proposal hypothesizes that distinct interactions of G? and GIRK channels contribute to distinct effects of G? on GIRK currents. Specifically, G? -mediated effects on GIRK currents examined in this proposal are the stimulation of basal/agonist-induced currents and potentiation of Na+-induced currents. Simulations done in silico are used to predict pairs of interacting surface residues between the GIRK channel and G?. Validation of these predicted interaction sites and quantification of their relative contribution to various G? mediated effects on channel activity are accomplished through site directed mutagenesis and electrophysiological recordings. Findings will lead to a greater understanding of G protein signaling and the structural mechanism by which G? is able to independently control various activities of the same effector. G protein signaling is found ubiquitously throughout the body and controls various physiological phenomena. Most drugs sold today directly or indirectly modulate G protein signaling. Thus enhanced knowledge of the structural mechanisms underlying this signaling may reveal further targets for manipulation by therapy.